Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR FORMING SHAPED ARTICLES
FIELD OF THE INVENTION
The invention relates to apparatus and methods for production of shaped
articles,
more particularly to apparatus and methods for performing a number of stamping
andlor punching operations on a strip of material.
BACKGROUND OF THE INVENTION
Heat exchangers are commonly formed from stacks of flat plates. In such heat
exchangers, spaces between adjacent plates define internal flow passages. Heat
exchangers of this type are described in U.S. Patent Nos. 5,794,691 (Evans et
al.)
and 6,244,334 (Wu et al.). This type of stacked plate construction is also
used in fuel
cells and electrolyzers. In these applications, individual plates (bipolar
plates) may
be bonded together in pairs containing spaced apart passages for coolant flow
between them, and outer facing passages for reactant fluid flow. The bipolar
plate
pairs are then assembled into a stack comprising catalvyst-coated membranes
and
gas diffusion layers sandwiched between each of the bipolar plate pairs. The
plates
described herein are typically metal, although other materials such as
conductive
composite polymer materials may also be used.
For metallic constructions, each individual plate in a stacked plate heat
exchanger or
fue! cell may be formed. by a plurality of separate punching and/or stamping
operations performed by one or more different devices. For example, the plates
can
be formed from a strip by punching apertures, bosses andlor other
discontinuities in a
central portion of the plate and then passing the strip through a progressive
stamping
die to form the periphery of the plate and to separate it from the strip. The
strip may
be unwound from a coil and incrementally fed to the punching apparatus by a
feed
mechanism having one or more feed rollers.
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In such operations it is difficult to ensure that the discointinuities formed
by the
various punching operations are properly spaced from each other and from the
periphery of the plate: In particular, small errors in feeding the strip are
repeated for
each incremental advance of the strip. These errors are compounded during the
course of a production cycle and may result in parts which do not meet
specifications
and must be scrapped or may contribute to small increimental assembly errors
that
are initially undetected but can result in decreased product yield in the
downstream
assembly process, resulting in even greater losses.
Moreover, traditional progressive dies can be extremely expensive for plates
that
require forming sections to produce the intricate patterns of formed channels
and
bosses typically required for fluid passages in the intended product
applications.
Finally, in some heat exchanger constructions and most fuel cell
constructions,
optimum functional design requires dissimilar plates to be joined alternately
in the
assembled stack. Such dissimilar plates often have common peripheral features
for
bonding but have different form sections (different charnel patterns or
channel
heights), or different manifold boss or other internal feature locations or
heights. In
the case of fuel cell constructions for instance, separate anode and cathode
plates
are required, which may require substantially different geometric features and
channel heights. To produce products of this type by conventional means, two
different progressive dies must be purchased at a substantial cost increment.
Moreover to maintain balanced production flow in a continuous production
setting,
the two dies would need to be run in parallel on two prEases, further
compounding
the cost and complexity of operation. To date, it has not been possible to
produce
different types of plates from a single strip of material, in a mass
production
environment, without using complex and expensive manufacturing equipment as
described above
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The need exists for apparatus and methods which are able to accurately perform
a
plurality of punching and/or stamping operations and which permit efficient
production
of different types of plates from a single strip of material, preferably using
low cost
tooling equipment which allows the production of different or alternating
types of parts
in a balanced production flow process.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an apparatus far forming a
plurality of
shaped articles from a strip of material, the apparatus comprising: a feed
mechanism
for incrementally feeding the strip of material in a forward direction along a
strip feed
axis; a forming device which receives the strip of material from the feed
mechanism
and which forms discontinuities in the strip of material at axially-spaced
intervals; an
alignment device for maintaining constant axial spacing between the
discontinuities,
the alignment device being located in fixed axial relation to both the forming
device
and the feed mechanism, the alignment device comprising a frame structure
having a
first portion and a second portion between which the strip is fed, the first
and second
portions being movable toward and away from one another, a pilot hole punch
for
forming pilot holes in the strip and a pilot pin rigidly mounted in axially-
spaced relation
to one another on the first portion of the frame structure, the pilot pin
being spaced
forward of the pilot hole punch so that the pilot pin is insertabie into a
pilot hole
previously formed by the punch; wherein the pilot pin and the pilot hole punch
each
have a length such that when the first and second portions of the frame
structure are
moved toward one another, the pilot pin passes through a pilot hole before the
punch
contacts the strip and aligns the strip relative to the pilot hole punch and
the forming
device.
In another aspect, the present invention provides a method for forming a
plurality of
shaped articles from a strip of material, comprising the following steps:
incrementally
feeding the strip of material in a forward direction along a strip feed axis;
forming
CA 02466688 2004-04-30
discontinuities in the strip of material at axially-spaced intervals;
periodically aligning
the strip to maintain constant axial spacing between the discontinuities by
use of an
alignment device comprising a frame structure having a first portion and a
second
portion between which the strip is fed, the first and second portions being
movable
toward and away from one another, the alignment device including a pilot hole
punch
and a pilot pin rigidly mounted in axially-spaced relation to one another on
the first
portion of the frame structure; after each said incremental feeding step,
moving the
first and second portions of the frame structure toward one another, thereby
causing
the pilot hole punch to punch a pilot hole in the strip and to simultaneously
cause the
pilot pin to pass through a pilot hole previously formed by the pilot hole
punch;
wherein the pilot pin and the pilot hole punch each have a length such that,
during
movement of the first and second portions of the frame: structure toward one
another,
the pilot pin passes through a pilot hole before the punch contacts the strip,
and the
pilot pin thereby aligns the strip relative to the pilot hole punch.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example only, with reference to
the
accompanying drawings in which:
Figure 1 is a perspective view of an apparatus according to a first preferred
embodiment of the invention;
Figure 2 is a side elevation view of the apparatus of Fic,~ure 1;
Figures 3 to 10 are schematic side elevations showing a preferred alignment
device
according to the invention; and
Figure 11 is a perspective view of stamped strip stock laroduced using a
preferred
method and apparatus according to the invention.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figures 1 and 2 illustrate a preferred apparatus according to the present
invention.
Apparatus 10 unwinds a flat strip 12 of a material such as sheet metal from a
coil 14
and converts it through a plurality of punching and stamping operations to a
shaped
article which, in the drawings, comprises a dished plate 16 for a heat
exchanger.
Examples of patents describing dished plate heat exchangers include U.S.
Patent
Nos. 5,291,945 (Blomgren et al.) and 6,182,746 (Wiese et al.).
As shown in Figure 11, the plate 16 has a periphery 18 provided with a side
wall 20
and a central portion 22. The central portion 22 is provided with one or more
discontinuities which, in the context of dished plate production, are
typically selected
from one or more members of the group comprising ribs, dimples, holes and
raised
apertured bosses. These discontinuities are typically formed by punching,
stamping
or drawing the sheet metal strip 12 using one or more punches andlor dies. It
will,
however, be appreciated that other types of discontinuities can be formed in
the strip
12. For example, discontinuities can be formed by welding other components
onto
the strip or by cutting or bending the strip.
In the preferred embodiment shown in the drawings, the central portion 22 of
plate 16
is provided with two holes 24 and two raised apertured bosses 26. A heat
exchanger
(not shown) can be formed by stacking plates 16 one on top of each other in a
conventional manner, as described in the Blomgren et al, and Wiese et a(.
patents
mentioned above. .
The apparatus 10 further comprises a feed mechanism 28 for incrementally
feeding
the strip 12 of material in a forward direction (as shown by arrows A and B)
along a
strip feed axis S. The feed mechanism 28 is schematically illustrated in the
drawings
as comprising an upper feed roller 30 and a lower feed roller 32 between which
the
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strip 12 passes. The feed rollers 30, 32 are mounted in a frame member 33
which is
provided with an engagement mechanism 34 for moving the rollers 30 and 32
toward
and away from one another in the directions indicated by double-ended arrow C.
As would be apparent to one skilled in the art, the strip 12 is incrementally
advanced
in the forward. direction (arrow B) when engaged along its op and bottom
surfaces by
the upper and lower rollers 30, 32 and with rollers 30,32 rotating as
indicated in
Figures 3, 5 and 10. Similarly, the strip 12 is released from engagement with
feed
mechanism 28 when rollers 30, 32 are moved away frc>m one another.
As it is unwound from roller 14 by the feed mechanism 28, the strip 12 is fed
axially
along a feed table 36 to a first forming device 38 which forms discontinuities
in the
strip 12 of material at axially-spaced intervals. Preferably, the first
forming device
comprises a frame structure 40 having an upper arm 41 and a lower arm 42 which
are substantially parallel to one another and are connected together at their
ends by
a pair of side members 47, 49. The frame structure 40 is supported to
reciprocate
laterally of the strip feed axis S (in the directions indicated by arrows D
and E). As
shown in Figure 1, the lower arm 42 of frame structure 40 may preferably be
supported by a stationary beam 43 along which it can be moved laterally. A
reciprocating drive (not shown) is provided for reciprocating the frame
structure 40
laterally of the strip feed axis S along beam 43.
A plurality of tools for forming discontinuities in the strip 12 are supported
on the
upper arm 41 of the frame structure 40. Ln the preferred embodiment shown in
the
drawings, in which the discontinuities comprise holes 24 and bosses 26, the
tools
comprise punches 44. A total of four punches 44 are illustrated in the
drawings.
However, it will be appreciated that more or fewer punches 44 may be required,
depending on the form and orientation of the discontinuities in the article
16. In the
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embodiment shown in the drawings, one of the punches 44 is for forming the
holes
24 while the other three punches 44 are for forming and shaping the bosses 26.
Each of the punches 44 is actuated by a punch actuator mechanism 45 which, in
the
preferred embodiment shown in the drawings, comprises a pneumatic cylinder 46
having a piston 48 pivotably connected to a bell crank ;a0. As shown in Figure
2,
each bell crank 50 is pivotable about a fixed point 51 and is connected to its
associated punch 44 through a pivoting connecting arm 52.
Located directly under the frame structure 40 and under strip 12 is a lower
die block
53 which is provided with a plurality of die buttons 54, each of which mates
with one
of the punches 44.
As will be appreciated, the provision of multiple punches 44 on the
transversely
reciprocating frame structure 40 provides great flexibility and enables the
formation of
various configurations of discontinuities in the central portions 22 of plates
16. For
example, a controller (not shown) may be programmed so that the punches 44
form
different configurations of discontinuities in alternating plates 16.
Therefore, the
apparatus of the present invention conveniently permit:> the production of two
or more
different plates from a single strip 12 of material.
In addition to forming different configurations of discontinuities on
alternating plates,
the apparatus according to the invention also has the ability to produce
discontinuities of different heights on alternating plates. This is
advantageous, for
example, in the manufacture of anode and cathode plai:es for use in fuel
cells.
Typically, the anode and cathode plates are provided with different rib
patterns and
channels of different height. The provision of different channel heights in
alternating
plates can be accomplished by several methods, including the use of a
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programmable, variable stroke press or by using an additional die on
alternating
plates to provide greater channel height.
The apparatus according to the invention may also include one or more
additional
forming devices. In the preferred embodiment shown iin the drawings, a second
forming device 56 is provided. Forming device 56 preferably comprises a
stamping
apparatus and, as shown in the drawings, more preferably comprises a
progressive
stamping die for forming the peripheries 18 of plates 16 and for separating
the plates
16 from the strip 12. The second forming device 56 includes an upper stampivg
die
58 and a lower stamping die 60. Where the second forming device 56 comprises a
progressive stamping apparatus, the dies 58, 60 preferably comprise a
plurality of
stamping stations 62, 64, 66 and 68 in which features of the periphery 18
and/or
central portion 22 of plate 16 are progressively stamped. It will be
appreciated that
the number of stamping stations in the progressive stamping apparatus may vary
from that shown in the drawings.
The second forming device includes a mechanism 78 for opening and closing the
dies 58, 60 in the directions indicated by double-ended arrow F (Fig. 1 ). As
shown in
the drawings,, the mechanism 78 may comprise hydraulic cylinders 80 having
pistons
82 which act on a block 84 carrying the upper stamping die 58.
The apparatus according to the invention also comprises an alignment device 85
for
maintaining constant axial spacing between the discontinuities formed in strip
12. In
order to maintain constant spacing, the alignment device 85 is located in
fixed axial
relation to the first and second forming devices 38, 56 <~nd to the feed
mechanism 28.
The alignment device 85 is schematically illustrated in the drawings as
comprising an
upper die 86 and a lower die 88 between which the strip 12 is fed. The dies 86
and
88 are mounted in a frame member 118 which is provided with a hydraulic
cylinder
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120 or similar means to open and close the dies 86 and 88. As shown in Figures
3 to
10, the upper and lower dies are movable toward and away from one another.
As shown in Figure 3, the upper die 86 of the alignment device 85 may
preferably
comprise a pair of die plates, including a first die plate 90 and a second die
plate 92
biased apart by a coil spring 94 or other suitable biasing means. The first
die plate
90 carries a pilot hole punch 96 and a pilot pin 98 and the second die plate
92 is
provided with apertures 100 and 102 through which the pilot hole punch 96 and
pilot
pin 98 can move reciprocally as described below.
Figure 3 illustrates the first step of a production cycle, in which an end of
the strip 12
is fed by rollers 30, 32 to the first forming device 38. As illustrated in
Figure 3, when
the rollers 30, 32 of feed mechanism 28 engage the strip 12 and are rotated as
-
indicated by arrows H and l, the strip 12 is advanced by an incremental amount
in the
direction shown by arrow G. The forward end of the strip becomes received
between
the upper and lower dies 86, 88 of the alignment device 85: The upper and
lower
dies 86, 88 are open to permit feeding of the strip:
As shown in Figure 4, rotation of the rollers 30, 32 is discontinued in order
to stop
incremental feeding of the strip 12, but the rollers 30, 32 remain in
engagement with
the strip 12. The upper die 86 of the alignment device 85 is then brought down
to
punch a pilot hole 104 in the strip 12. The plug 106 removed by the punch 96
is
preferably.ejected from the apparatus 85. As shown in Figure 4, the pilot hole
punch
96 preferably extends into an aperture 108 in the lower die 88 when the upper
and
lower dies 86 and 88 are closed.
Following formation of the pilot hole 104, the dies 86 and 88 are opened and
rollers
and 32 are again actuated to cause forward feeding of the strip by an
incremental
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amount as shown in Figure 5. Feeding of the strip 12 its discontinued once the
strip
reaches the position shown in Figure 6.
As can be seen from Figure 6, the incremental amount by which strip 12 is fed
corresponds to a distance between the pilot hole puncll and the pilot pin,
causing the
pilot hole 104 to become aligned with the pilot pin 98. However, due to
feeding
errors, the pilot hole 104 may not be precisely aligned with the pilot pin 98.
The
magnitude of the misalignment shown in Figure 6 may be exaggerated. In Figure
6,
the rollers 30,32 have advanced the strip 12 slightly too far forward. If left
uncorrected, these feeding errors would lead to inaccuracies in the locations
of the
discontinuities which would be compounded over the course of a production
cycle.
The strip 12 is brought back into alignment as shown in Figures 7 and 8.
First, rollers
30, 32 are disengaged from the strip 12, for example by withdrawing one or
both
rollers 30,32 away from the strip 12. Figure 7 shows roller 30 being withdrawn
in an
upward direction in order to disengage the strip 12. During or after
disengagement of
the strip from rollers 30, 32, the upper and lower dies 8'.6 and 88 of the
alignment
device are again closed. As can be seen in Figure 7, the relative lengths of
the pilot
pin 98 and the pilot hole punch 96 are such that when llhe upper and lower
dies 86,
88 of the alignment device are moved toward one another, the pilot pin
contacts the
strip 12 first and passes though the previously formed pilot hole 104 before
the punch
96 contacts the strip 12. The pilot pin 98 has a rounded tip 99 which contacts
the
edge of the pilot hole 104, causing movement of the strip until it is
precisely aligned
with the pin 98. The pin 98 then passes through the pilot hole 104 to be
closely
received inside an aperture 110 in the lower die 88 of alignment device 85. As
will be
appreciated, the disengagement of feed mechanism 28 permits the strip to be
moved
by a small distance either backward as shown in Figure 7, forward or
laterally. In
order to provide effective alignment, the pilot hole punch 96 and pilot pin 98
are
preferably of substantially the same diameter.
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After the strip 12 is aligned as shown in Figure 8, the upper and lower dies
86 and 88
continue to close and the pilot hole punch 96 is then brought into contact
with the
strip 12 so that a second pilot hole 104' is formed in the strip 12 and a
second plug
106' is ejected from the device 85. It will be appreciated that the distance
between
pilot holes 104 and 104' corresponds exactly to the distance between the pilot
hole
punch 96 and the pilot pin 98. Following formation of the second pilot hole
104', the
upper and lower dies 86, 88 of device 85 are open and the rollers 30, 32 of
feed
mechanism 28 are again brought into engagement with the strip for further
incremental movement. It will also be appreciated that the rollers 30, 32 may
be
brought into engagement with the strip 12 before opening of the dies 86 and
88. For
example, the rollers 30, 32 can be brought into engagement with strip 12
during or
immediately after formation of pilot ho1e104', and immediately after alignment
of the
strip 12 by the pilot pin 98.
The steps illustrated in Figures 6 to 10 are then repeated for each
incremental
movement of the strip 12, such that a series of precisely aligned pilot holes
104 are
formed along the length of the strip 12. The pilot holes 104 can be seen in
the strip
12 shown in Figure 11. As illustrated, pairs of pilot holes 104 are preferably
formed
at regularly spaced intervals along opposite edges of the strip 12.
The alignment device 85 may be located at any one of a number of different
locations
along the strip feed axis S. In the preferred embodiment shown in Figures 1
and 2,
the alignment device 85 is located between the feed mechanism 28 and the first
forming device 38 and is mounted on the same base 112 as the first forming
device
38. In the alternative, the alignment device 85 may preferably be located
between
the first and second forming devices 38, 56 or it may be incorporated into
either the
first or second forming device 56. For example, where the second forming
device is
a progressive stamping apparatus, the alignment device 85 may preferably be
located at a first stamping station of the apparatus. The alignment device 85
may
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also comprise a self-contained unit which may be movable relative to the other
components of the apparatus.
Figure 11 illustrates the appearance of strip 12 as it is conveyed through an
apparatus 10 such as that illustrated by Figures 1 and :Z, comprising a first
forming
apparatus 38, a progressive stamping die 56 and an alignment device 85. The
portion of strip 12 shown in Figure 11 is divided into segments A to G in
order to
identify the various forming operations according to the invention.
Since the alignment device 85 is located ahead of both the first and second
forming
apparatus 38, 56 in Figure 1, the first feature formed in strip 12 is the
pilot hole 104.
This is illustrated at segment A of the strip 12 shown in Figure 11. The pilot
hole 104
is formed as shown in Figs. 4 and 8 by the pilot hole punch 96 of the
alignment
device 85. In order to permit alignment of the strip 12, it is preferred that
the
progressive stamping die 56 be open during alignment of the strip 12 and
formation
of pilot holes 104.
Next, at segment B of the strip 12, discontinuities are formed in the central
portion of
the strip 12 by the first forming device 38. In the preferred embodiment of
the
invention, the discontinuities comprise a pair of laterall,r spaced holes 24
and a pair
of laterally spaced bosses 26, the center-to-center distance between the holes
24
and the bosses 26 corresponding to a distance L1 and the center-to-center
distance
between the holes of one plate and the basses of an adjacent plate
corresponding to
distance L2.
Following formation of a pilot hole 104 by the pilot hole punch 9C, the strip
12 is fed
forwardly along the axis S by an incremental amount L2, following which the
holes 24
are formed by one of the punches 44 of the first forming device. It is to be
noted that
the holes 24 are formed with the rollers 30, 32 of the feed mechanism 28
engaging
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the strip 12. Following formation of holes 24, the strip 12 is advanced by
amount L1
and the bosses are formed by one or more of the other punches 44 of the first
forming device 38. The bosses 26 are preferably formed in three steps; pre-
piercing,
forming and final piercing. During formation of the bosses 26, another pilot
hole 104
is punched by the alignment device 85. Thus, the strip 12 is advanced by an
amount
L1 + L2 for each alignment operation, so that only one set of pilot holes is
punched
for each plate.
After formation of the holes 24 and bosses 26, the remaining forming
operations,
shown at segments C to G of Figure 11, are performed by the progressive
stamping
apparatus 56. Preferably, the closing of the progressive stamping die 56 is
synchronized with the operation of the alignment device 85 such that the dies
of the
progressive stamping apparatus 56 close immediately after alignment of the
strip 12
by the pilot pin 98. As with the alignment device 85, the strip 12 is advanced
by an
amount L1 + L2 for each 'progressive stamping operation. The progressive
stamping
apparatus 56 is preferably provided with index pins 70 which engage the pilot
holes
104 and maintain proper alignment of the strip as it passes through the
progressive
stamping apparatus.
Although the invention has been described in connection with certain preferred
embodiments, it is not limited thereto. Rather, the invention includes all
embodiments which may fall within the scope of the following claims.
